For example, in video produced as a moving image like TV broadcasting, usually a large number of frame images consecutive in time series are switched in sequence at given time intervals (for example, 1/60-second frame period) for output. However, to switch a scene in the same program or to switch the program, the continuity of the frame images output in sequence is interrupted suddenly and thus there is a possibility that an unnatural sense may be given to the viewer. In such a case, gradual switching is performed from a frame image of the preceding scene to a frame image of the following scene, whereby the viewer can be reliably informed of scene transition.
At the switching time, two areas are formed in the same screen and the frame image of the scene before the switching is displayed in one area and the frame image of the scene after the switching is displayed in the other area, whereby it is made possible to inform the viewer of scene switching more clearly. As the boundary of more than one area on such a screen, it is possible to use a straight line as a simplest example, but effective scene switching can be accomplished by selectively using patterns of various shapes. To generate such a boundary pattern, a wipe pattern generation apparatus is used.
For example, an art disclosed in patent document 1 is known as an art concerning a wipe pattern generation apparatus in a related art. This kind of wipe pattern generation apparatus switches two video inputs for display in response to the value of the comparison result between the distance of each position from the center coordinates on the screen and a threshold value using coordinate information representing each position on the display screen as polar coordinates.
The wipe pattern generation apparatus in the related art includes a polar coordinate conversion section 803, pattern memory 806, a multiplier 808, and a comparator 809, for example, as shown in FIG. 26. Coordinates representing a scan position on a display screen as shown in FIG. 27 are input to the polar coordinate conversion section 803 as a combination of an x coordinate 801 and a y coordinate 802. The x coordinate 801 represents a pixel position in a horizontal direction on the screen and the y coordinate 802 represents a pixel position in a vertical direction on the screen.
In fact, scanning is executed in the order of (1), (2), (3), and (4) about each scan line shown in FIG. 27 and the current scan position is input to the polar coordinate conversion section 803 as a combination of the x coordinate 801 and the y coordinate 802. The polar coordinate conversion section 803 converts the input combination of the x coordinate 801 and the y coordinate 802 into position information of polar coordinate representation.
In the wipe pattern generation apparatus, in the polar coordinate representation, the coordinates of each position are represented by angle θ and distance r. That is, with a predetermined polar coordinate origin 811 as the center, the coordinates are represented by a combination of a θ coordinate 804 of the angle θ representing an inclination relative to the reference axis and an r coordinate 805 representing the distance r from the polar coordinate origin 811 to each position, as shown in FIG. 28.
The pattern memory 806 retains information of the r coordinate 805 representing the distance r from the polar coordinate origin 811 in each address associated with the θ coordinate 804. That is, the pattern memory 806 retains as pattern data corresponding to a predetermined pattern the value corresponding to the distance r from the polar coordinate origin 811 to each point on the contour of a wipe pattern to generate the pattern for each angle θ. Therefore, if the θ coordinate 804 is input to the pattern memory 806 as a read address, the pattern data representing the distance in the corresponding direction is read from the pattern memory 806.
The multiplier 808 multiplies the pattern data representing the distance read from the pattern memory 806 by an externally input coefficient 807 to scale up/down a generated wipe pattern and outputs the result. The comparator 809 makes a comparison between the value output by the multiplier 808 and the value of the r coordinate 805 output from the polar coordinate conversion section 803 and outputs the comparison result as wipe pattern output 810. The wipe pattern output 810 output from the comparator 809 is binary data and represents which of the outside and the inside of the wipe pattern contour the position of each point exists in.
For example, if data representing a pattern of a triangle is stored in the pattern memory 806, the pattern data representing the distance from the polar coordinate origin 811 to each point on the contour of the triangle pattern is read from the pattern memory 806 in response to the input value of the θ coordinate 804, as shown in FIG. 29. Since the pattern data read from the pattern memory 806 is multiplied by the coefficient 807 by the multiplier 808, pattern scaling up or down processing can be performed by the multiplication.
In fact, a display screen is scanned in sequence and position information of each scan position is input to the polar coordinate conversion section 803 as a combination of the x coordinate 801 and the y coordinate 802 and therefore the wipe pattern output 810 output from the comparator 809 becomes as shown in FIG. 30. That is, whether the position of each point is in the inside or the outside of the contour with the contour of the triangle pattern as the boundary is determined and the display screen is partitioned into two regions as indicated by hatch lines and a white background in the figure.    Patent document 1: JP-A-10-65966